Area of Habitat maps for the world’s terrestrial birds and mammals

Knowing the distribution of species is crucial for effective conservation action. However, accurate and high-resolution spatial data are only available for a limited number of species^1,2. For mammals and birds, the most comprehensive and widely used global distribution dataset is the set of range maps compiled as part of the assessments for the International Union for Conservation of Nature (IUCN) Red List. These represent each species’ distributional limits and tend to minimize omission errors (i.e. false absences) at the expense of commission errors (i.e. false presences)^3,4. Therefore, they often contain sizeable areas not regularly occupied by the species.

Maps of the Area of Habitat (AOH; previously known as Extent of Suitable Habitat, ESH) complement range maps by indicating potential occupancy within the range, thereby reducing commission errors⁵. AOH is defined as ‘the habitat available to a species, that is, habitat within its range’⁵. These models are produced by subtracting areas unsuitable for the species within their range, using information on each species’ associations with habitat and elevation^5,6,7,8. Comprehensive sets of AOH maps have been produced in the past for mammals⁶ and amphibians⁷, as well as subsets of birds^8,9. The percentage of a species’ range covered by the AOH varies depending on the methodology used to associate species to their habitats, and their habitats to land-cover, the coarseness of the range map, the region in which the species is distributed, and the species’ habitat specialization and elevation limits⁵. For example, Rondinini et al.⁶ found that, when considering elevation and land cover features for terrestrial mammals, the AOH comprised, on average, 55% of the range. Ficetola et al.⁷ obtained a similar percentage when analyzing amphibians (55% for forest species, 42% for open habitat species and 61% for habitat generalists). Beresford et al.⁸ found that AOH covered a mean of 27.6% of the range maps of 157 threatened African bird species. In 2019, Brooks et al.⁵ proposed a formal definition and standardized methodology to produce AOH, limiting the inputs to habitat preferences, elevation limits, and geographical range.

AOH production requires knowledge of which habitat types a species occurs in and their location within the range¹. Information on habitat preference is documented for each species assessed in the IUCN Red List¹⁰, following the IUCN Habitats Classification Scheme¹¹. However, the IUCN does not define habitat classes in a spatially explicit way, therefore, we used a recently published translation table that associates IUCN Habitat Classification Scheme classes with land cover classes¹². Species’ elevation limits were also extracted from the IUCN Red List.

We developed AOH maps for 5,481 terrestrial mammal species and 10,651 terrestrial bird species (Fig. 1). For 1,816 bird species defined by BirdLife International as migratory, we developed separate AOH maps, for the resident, breeding, and non-breeding ranges, according to the migratory distribution of the species (Fig. 2). The maps are presented in a regular latitude/longitude grid with an approximate 100 m resolution at the equator. On average, the AOH covers 66 ± 28% of the geographical range for mammals and 64 ± 27% for birds. We used the resulting AOH maps to produce four global species richness layers for: mammals, birds, globally threatened mammals and globally threatened birds¹³ (Fig. 3).

The AOH maps presented in this paper are more useful for some purposes than global species distribution models, as they reduce and standardize commissions¹⁴. They are especially useful for not well-known and wide-range species. However, we note that for well-known species alternative sources may have more accurate distributions¹⁵. Moreover, AOHs are affected by the bias and errors of the underlying data, especially relevant errors associated with documentation of species’ habitats and elevations, and the translation of habitats into land cover classes, given that habitat is a complex multidimensional concept that is challenging to match to land-cover classes¹², and that the current version of the IUCN Habitat Classification Scheme on IUCN’s website is described as a draft version¹¹.

The AOH maps have multiple conservation applications^5,16,17, such as assessing species’ distributions and extinction risk, improving the accuracy of conservation planning, monitoring habitat loss and fragmentation, and guiding conservation actions. AOH has been proposed as an additional spatial metric to be documented in the Red List⁵, and is used for the identification of Key Biodiversity Areas¹⁸.

Source: Ecology - nature.com